The domestic hot water heater is one of the highest energy consumers in the typical home. Contrary to the situation elsewhere in the world, most hot water installations in the Unites States store a pre-heated supply of hot water. Therefore, substantial energy consumption continues even during periods of no hot water usage. The amount of energy loss is a function of the difference between the temperature maintained by the water heater and the ambient temperature. The higher the system temperature, the higher the losses due to convection and conduction.
Most uses for domestic hot water require the temperature delivered to the outlet to be 110 degrees or less. For example, for showering, a typical person takes a shower with water temperatures of 110 degrees or less. Therefore, the only function of water heater system temperatures above 110 degrees for that purpose is to build a temperature reserve. With higher tank temperatures the person will mix hot and cold water causing the effective system capacity to increase.
Systems according to the prior art have recognized that substantial energy conservation benefits can be obtained by a reduction in the water heater system temperature during periods of non-use, and increasing the system temperature only when substantial water flow indicates a substantial prospective demand for hot water; and therefore, for system temperatures which create an energy reserve. However, such systems require a mechanical attachment to, and manipulation of the standard water heater controls; and are therefore not well suited to, or modification of the standard water heater thermostat control, or cannot benefit from, the integration into the water heater design itself.
Accordingly, an integrated usage dependent controller for gas water heaters is desirable, particularly where such an integrated gas water heater usage dependent controller does not disturb normal system functions including main thermostat gas control and vacation settings.